Method and apparatus for transmitting a frame synchronisation sequence and band extension information for a uwb multi-band cofdm wireless network

ABSTRACT

The present invention provides a mechanism for alleviating a latency problem of one of the proposals for a potential IEEE 802.15.3a standard. The invention places band extension information into the frame sync sequence, as per the evolving standard, but places channel estimation information together with that of the 3-band channel estimation information using the actual TF code ( 909 ). The PLCP header ( 308 ) is transmitted using the actual TF code ( 909 ) and interleaver.

The present invention relates to an alternative frame synchronizationsequence for wireless personal area networks.

System performance and spectral efficiency of ultra wide band (UWB)radio devices is an objective of ongoing research to determine thepractical limits of spatial capacity and other parameters. There is agrowing need for high data rates to transmit, e.g., video over air, andtodays short-range wireless systems based on narrow band carriermodulation are inadequate or incapable of such high data rates. UWBradio systems, using simple modulation and appropriate coding schemes,can transit at rates in excess of 100 Mbs over short distances achievinga high data rate (HDR). Alternatively, UWB radios can increase linkrange at the expense of data rate, which can be combined with accuratelocation tracking capabilities for low data rate and location tracking(LDR/LT) capabilities. These complementary usages can be implementedbased on architectures that are highly similar and have unprecedentedscalability.

Spectral flexibility of UWB devices provides robust performance in thepresence of narrowband interferers and co-location with other wirelessdevices. It also provides for operation in different regulatoryenvironments since only the U.S. has regulations for UWB in place today.The IEEE 802.15.3a task group has addressed “spectral flexibility” withrespect to how extensible Proposed implementations are at meetingdiffering or changing international regulations. Can UWB architecturesbe readily extended without changing the MAC or giving up backwardcompatibility to include newly allocated spectrum?

The FCC has ruled that UWB handheld devices may communicate with auniform power spectral density in the range 3.1-10.6 GHz. The IEEE802.15.3a standard is evolving to address potential cases where othercountries adopt modified emission requirements and where permitted bandsare added in the future.

One of the proposals to the IEEE 802.15.3a standardization task groupuses a multi-band OFDM system for UWB HDR wireless personal areanetworks (WPANs) having a maximum distance of 20.5 m in AWGN, andgreater than 11 m in multipath environments for a mode 1 device. Theproposal uses the frame sync sequence for band extension. For 3-band ormode 1, the preamble structure is illustrated in FIG. 1. For the 7-bandor mode 2, the header and the channel estimation extension (bandextension) are interleaved, see FIG. 2. The MAC handles an additionalband by assigning this new band to an already existing field in the MACthat already is there supporting the bands allocated today. The PHYhandles this change by adding the required transmitter and receivercircuitry to support the additional UWB band.

The band extension information is placed into the PHY header. Thechannel estimation information follows the PLCP header. The header isextended by 1 COFDM symbol 100. A 100-bit interleaver is used for thePLCP header, see FIG. 3.

The proposal has several advantages: the number of reserved bits hasincreased from 2 to 7; the number of tail bits for the PLCP header hasincreased; and, the number of RATE bits has increase from 3 to 4 so that16 data rates can be supported.

However, the evolving IEEE 802.15.3a proposal also has severaldisadvantages: it constrains the design of the receiver by placingchannel estimated after the PLCP header; and, depending on the design ofthe receiver, there is a potential latency problem. There is some lossof burst error performance due to the use of the 100-bit interleaver.The PLCP header is still transmitted over 3 bands even though 7 bandsare available with the result that there is a potential SOP performanceimpact on the PLCP header. Finally, for small size packets there is animpact on throughput, but this impact is minor for long packets.

With respect to the potential for a latency problem, referring now toFIG. 4, if channel estimation takes about 9 OFDM symbol times, a latencyof at least 1 OFDM symbol time will result and, thus, there will not besufficient time to close the loop to the mixer. The receiver design mustbe highly constrained to meet the latency requirement. This compromisesperformance.

The present invention provides a mechanism for alleviating theabove-described latency problem of the proposed IEEE 802.15.3a proposal.The invention places band extension information into the frame syncsequence, as per the proposed standard, but places channel estimationinformation together with that of the 3-band channel estimationinformation using the actual TF code. The PLCP header is transmittedusing the actual TF code and interleaver.

In a preferred embodiment, for each symbol, one out of four possiblesignals is transmitted as a frame sync by using one of three possibleoptions for the frame sync sequence which is spread using a sequence oflength 8.

This approach eliminates the latency problem with no change ofstructure, provides a seamless processing of channel estimation and PLCPheader decoding with no increase in the PLCP header information and isas reliable as detecting the frame sync.

FIG. 1 illustrates a PLCP preamble for Mode 1 (3-band) device;

FIG. 2 illustrates a PLCP preamble for Mode 2 (7-band) device;

FIG. 3 illustrates the IEEE 802.15.3a proposed packet format,highlighting the format of the PHY header;

FIG. 4 illustrates a latency analysis of the IEEE 802.15.3a draftproposal;

FIG. 5 illustrates the packet structure of the present invention;

FIG. 6 illustrates a PLCP preamble for Mode 1, according to anembodiment of the present invention;

FIG. 7 illustrates a PLCP preamble for Mode 2 (7-band), according to anembodiment of the present invention;

FIG. 8 illustrates the IEEE 802.15.3 draft preamble pattern;

FIG. 9 illustrates an embodiment of a transceiver according to anembodiment of the present invention;

FIG. 10 illustrates correlation output for time-domain sequence fromactual simulation in an ideal channel, 110 Mb/s for a transmitted framesync sequence: flip (A), flip (A1);

FIG. 11 illustrates simulation results for AWGN channel and 1 dB Eb/NO,110 Mb/s mode; and

FIG. 12 illustrates simulation results for CM4-1 and 6 dB Eb/NO, 110Mb/s mode.

It is to be understood by persons of ordinary skill in the art that thefollowing descriptions are provided for purposes of illustration and notfor limitation. An artisan understands that there are many variationsthat lie within the spirit of the invention and the scope of theappended claims. Unnecessary detail of known functions and operationsmay be omitted from the current description so as not to obscure thepresent invention.

In the evolving IEEE 802.15.3a proposal, the PLCP preamble is designedto allow both Mode 1 (3-band) and Mode 2 (7-band) devices to operate inthe same piconet. Therefore, all devices in the same piconet must beable to detect the preamble and demodulate the PHY/MAC header of thePLCP header.

Referring now to FIG. 3, the system and method of the present inventionplaces band extension information into the frame sync sequence, as perthe evolving IEEE 802.15.3a standard, but places channel estimationinformation together with that of the 3-band channel estimationinformation using the actual time frequency (TF) code. The PLCP headeris transmitted using the actual TF code and interleaver, as illustratedin FIGS. 5-7.

For each symbol, one our of four possible sequences A=(A1, A2, A3, A4)is selected as a frame sync and transformed using one of three possibleoptions:

-   -   1. time-flipping, i.e., sending the last first and the first        last;    -   2. phase inversion; and    -   3. using one of the time-flipped version of A=(A1, A2, A3, A4)        with a pre-determined exclusion.        The transformed selection is then spread using one of four        possible sequences B=(B1, B2, B3, B4) of length 8, see FIG. 8 a.

Six bits of information can be transmitted by the frame sync symbols. Ina preferred embodiment, a simple rate ½ code is used to improveperformance. In one embodiment this is spreading three bits across threebands. In an alternative embodiment, just three bits of information aretransmitted.

A preferred embodiment uses the preamble-sensing hardware with minoradditional hardware and for CCA parallel scanning of the preamble may beperformed. Implementation is greatly eased because channel estimation iscontiguous.

The actual TF code is used during both channel estimation and PLCPheader decoding. This TF code is known a priori since it is related tothe preamble sequence.

The present invention eliminates the latency problem of the evolvingstandard discussed above with no change of structure, provides seamlessprocessing of channel estimation and PLCP header decoding with noincrease in the PLCP header information, and is a reliable as detectingthe frame sync.

FIG. 9 illustrates a block diagram of an example system architectureincorporating an embodiment of the present invention. As shown in FIG.3, the PLCP preamble 301 is sent first, followed by the PLCP header 302,followed by an optional band extension sequence 303, followed by theframe payload 304, the FCS 305, the tail bits 306, and finally the padbits 307. The PLCP header 302 is always transmitted using Mode 1. Theremainder of the PLCP frame (frame payload 304, FCS 305, tail bits 306,and pad bits 307) is sent at the desired information data rate of 55,80, 110, 160, 200, 320, or 480 Mb/s using either Mode 1 or Mode 2. Ifthe frame payload 304 is transmitted using Mode 2, then an optional bandextension field follows the PLCP header 302. The optional band extensionfield 303 is not used when the frame payload 304 is transmitted usingMode 1.

A typical OFDM transceiver comprises an Antenna 910 for sending anreceiving signal received from and provided to an RF/Analog section 904that is operably coupled to a Digital PHY section 905 which, in turn,delivers data 907 to a MAC section 906 and received data 908 therefrom.

Simulation results are illustrated in FIGS. 10-12. FIG. 10 illustratescorrelation output for time-domain sequence from actual simulation in anideal channel, 110 Mb/s for a transmitted frame sync sequence of flip(A1), flip (A1), (−A). This sequence exhibited very goodcross-correlation property (−21 dB isolation). FIG. 11 illustratessimulation results for AWGN channel and 1 dB Eb/NO, 110 Mb/s mode for atransmitted frame sync sequence of flip (A2), flip (A2), (−A1).Synchronization was possible, frame sync data was decodable, but payloaddata was not decodable at this SNR and channel. FIG. 12 illustratessimulation results for CM4-1 and 6 dB Eb/NO, 110 Mb/s mode for atransmitted frame sync sequence of flip(A2), flip(A2), (−A1).Synchronization was possible, frame sync data was decodable, but payloaddata was not decodable at this SNR and channel.

The transceiver and method of the present invention can be used forwireless personal area networks, for conveying video, audio, text,picture, and data, for controlling sensors, alarms, computers,audio-visual equipment, and entertainment systems. For example, thecontents of a digital camera can be downloaded to a computer wirelessly.

While the preferred embodiments of the present invention have beenillustrated and described, it will be understood by those skilled in theart that various changes and modifications may be made, and equivalentsmay be substituted for elements thereof without departing from the truescope of the present invention. In addition, many modifications may bemade to adapt the teachings of the present invention to a particularsituation without departing from its central scope. Therefore, it isintended that the present invention not be limited to the particularembodiments disclosed as the best mode contemplated for carrying out thepresent invention, but that the present invention include allembodiments falling within the scope of the appended claims. This isespecially pertinent due to the expected evolution of the UWB spectrumand is anticipated by the appended claims and is expressed in theforgoing disclosure.

1. A method of providing band expansion for a multi-band wireless personal area network, comprising the steps of: (a) including band extension information (300) in a PLCP header (308) of an encoded digital data stream; (b) after the PLCP header (308) of the encoded digital data stream, placing channel estimation information together with the 3-band channel estimation information using the actual time frequency code (909) (600) (700); (c) transmitting the encoded digital data stream across multi-bands that include the band extension; (d) using the actual time frequency code (909), decoding a PLCP header of a received encoded digital data stream that contains band extension information (905); and (e) demodulating (905) the multi-band stream using the band extension information of the decoded PLCP header.
 2. The method of claim 1, wherein the multi-band wireless personal area network is an ultra wide band coded orthogonal frequency division (UWB COFDM) network.
 3. The method of claim 1, wherein said including step (a) further comprises the step of (a.1) placing the band extension information into the frame sync sequence of the PLCP header (500).
 4. The method of claim 3, wherein said including step (a) further comprises the steps of: (a.2) for each symbol, selecting as a frame sync, one sequence of a first predetermined set of four sequences A=(A1, A2, A3, A4); (a.3) transforming the selected sequence using a mapping selected from the group consisting of time-flipping, phase inverting, and using one of the time-flipped version of (A1, A2, A3, A4) with a predetermined exclusion; and (a.4) spreading the transformed frame sync sequence using one sequence of a second predetermined set of four sequences B=(B1, B2, B3, B4).
 5. The method of claim 4, wherein: the frame sync comprises at most six bits of information; and a simple rate ½ code is used.
 6. The method of claim 5, wherein said simple rate ½ code comprises the step of (a.4.1) spreading three bits across three bands.
 7. The method of claim 5, wherein the frame sync comprises three bits of information.
 8. A method for extending the bands used by a multi-band transmitter, comprising the steps of: a) including band extension information (300) in the frame sync sequence of a PLCP header (308) of an encoded digital data stream; (b) after the PLCP header (308) of the encoded digital data stream, placing channel estimation information together with the 3-band channel estimation information using the actual time frequency code (909) (600) (700); and (c) transmitting the encoded digital data stream across multi-bands that include the band extension.
 9. The method of claim 8, wherein said including step (a) further comprises the steps of: (a.2) for each symbol, selecting as a frame sync, one sequence of a first predetermined set of four sequences A=(A1, A2, A3, A4); (a.3) transforming the selected sequence using a mapping selected from the group consisting of time-flipping, phase inverting, and using one of the time-flipped version of (A1, A2, A3, A4) with a predetermined exclusion; and (a.4) spreading the transformed frame sync sequence using one sequence of a second predetermined set of four sequences B=(B1, B2, B3, B4).
 10. The method of claim 9, wherein: the frame sync comprises at most six bits of information; and a simple rate ½ code is used.
 11. The method of claim 10, wherein said simple rate ½ code comprises the step of (a.4.1) spreading three bits across three bands.
 12. The method of claim 10, wherein the frame sync comprises three bits of information.
 13. A method for extending the bands used by a multi-band receiver, comprising the steps of: (a) using the actual time frequency code (909), decoding (905) a PLCP header of a received encoded digital data stream to obtain band extension information contained in the frame sync sequence; and (b) demodulating (905) the multi-band stream using the band extension information obtained from the decoded PLCP header.
 14. The method of claim 13, further comprising the step of (c) for clear channel assessment (CCA), performing parallel scanning of the PLCP preamble (308).
 15. A high-speed digital data stream of a plurality of symbols that are embodied in a carrierless ultra wideband signal, comprising: a PLCP preamble (301) including in a frame sync sequence thereof a first band extension information; a PLCP header (308) including in a PHY header (309) thereof a second band extension information (300) and at the end of said PLCP header including an optional third band extension information (303); wherein, said PLCP header (302) is transmitted using an actual time frequency (TF) code (909) and an interleaver.
 16. The signal of claim 15, wherein: for each symbol of said plurality, one our of four possible sequences A=(A1, A2, A3, A4) of length 16 is selected as a frame sync and transformed using one of three possible options:
 1. time-flipping, i.e., sending the last first and the first last;
 2. phase inversion; and
 3. using one of the time-flipped version of A=(A1, A2, A3, A4) with a pre-determined exclusion; and the transformed selection is then spread using one of four possible sequences B=(B1, B2, B3, B4) of length
 8. 17. The signal of claim 16, wherein: the frame sync comprises at most six bits of information; and a simple rate ½ code is used.
 18. The signal of claim 17, wherein said simple rate ½ code comprises spreading three bits across three bands.
 19. The signal of claim 17, wherein the frame sync comprises three bits of information.
 20. A transceiver for a carrierless ultra wideband signal embodying a high-speed digital data stream of a plurality of symbols, comprising: an antenna (910) for sending and receiving a UWB signal; an RF/Analog section (904) comprising an interleaver and operably coupled to the antenna for detecting a PLCP preamble (301) of the received signal, modulating and demodulating a PLCP header of the signal using an actual time frequency (TF) code (909) and said interleaver; a Digital PHY section (905) operably coupled to the RF/Analog section (904) and comprising a PLCP encoder/decoder (901) that uses the actual TF code (909) for (1) channel estimation (903), placing said channel estimation information together with that of a 3-band channel estimation information, and (2) PLCP header decoding, and that places band extension information into a frame sync sequence (902) of the PLCP preamble (301) and, optionally, after the PLCP header (308), selecting, transforming and spreading said frame sync; a MAC section (906) operably coupled to the Digital PHY section (905) for providing and input data stream (908) and receiving a demodulated and decoded data stream (907) therefrom.
 21. The transceiver of claim 20, wherein: for each symbol of said plurality, one our of four possible sequences A=(A1, A2, A3, A4) of length 16 is selected as a frame sync and transformed using one of three possible options:
 1. time-flipping, i.e., sending the last first and the first last;
 2. phase inversion; and
 3. using one of the time-flipped version of A=(A1, A2, A3, A4) with a pre-determined exclusion; and the transformed selection is then spread using one of four possible sequences B=(B1, B2, B3, B4) of length
 8. 22. The signal of claim 21, wherein: the frame sync comprises at most six bits of information; and a simple rate ½ code is used.
 23. The signal of claim 22, wherein said simple rate ½ code comprises spreading three bits across three bands.
 24. The signal of claim 23, wherein the frame sync comprises three bits of information. 